The Type-S meter is designed so that its terminals appear as short, rigid, copper contact blades extending outward from the back of the meter. To connect this meter to line and load wires, an auxiliary mounting device is required. This device is the meter socket.

The socket comprises connectors for line and load conductors, contact jaws to receive the meter terminal blades (thus completing connections between conductors and meter coils), and an enclosure for the whole assembly.

Early sockets were round, cast or drawn shallow pans with diameters matching those of the meters. In this type socket, wiring space was limited. This limitation led to the development of the rectangular-shaped trough with a round opening the diameter of the meter.

A sealing ring, which fitted around the meter rim and socket cover rim, secured the meter in place. More recently a ringless type of socket has been developed in which the socket cover opening fits over the meter after the meter has been installed.

The socket cover is then sealed in place to provide protection. In both types the primary functions are to: (1) fix the meter firmly on the socket; (2) close the joint between the meter and socket rim against weather and tampering; and (3) provide means for sealing the meter against unauthorized removal of the meter or cover.

Meter sockets are available in continuous duty current ratings of 20, 80, 100, 120, 150, 160, 200, 320, and 400 amperes and for one, two, or three stator meters. The requirements for indoor and outdoor service differ.

Meter sockets installed on the outside of the house must not only be weatherproof but must be of a material that is highly resistant to corrosion. Under some conditions, such as leakage of pipe joints or cable assemblies, sockets will accumulate varying quantities of water. To guard against water accumulation, sockets are provided with a means for drainage.

Obviously the dimensions of both meters and sockets must be standardized and closely controlled so that meters of any of the major American manufacturers will fit all sockets. The ANSI and NEMA standards have developed standards for meter and socket sizes. The Meter and Service Committees of EEI and AEIC have agreed upon certain basic requirements applicable to meters and the associated mounting devices.

The basic requirements are:
1. Interchangeability of all manufacturers’ meter mounting devices;
2.Mounting devices to be designed for single-meter or multiple-meter mounting either indoor or outdoor;
3. One seal to serve for both meter and mounting device;
4. Terminals to be inaccessible after the meter is sealed in place;
5.Meter base not to be insulated from the mounting device;
6.Mounting device to have an uninsulated terminal for the service neutral.

The material of the socket jaws is important. A tight contact between the meter connection blade and the contact surfaces of the jaw is necessary. This requires the use of an especially high-quality resilient copper alloy, which may be bronze or beryllium.

Even with the best-quality material, it must be remembered that spreading the jaws by pushing screwdriver blades into them may spring the metal beyond its elastic limit and destroy the tight contact with the meter blades.

It is also necessary that the connection between conductors and the line a nd load terminals be secure and of low resistance. The connectors in the lowerrated sockets may be required to accept conductors as small as No. 6 while the 200- and 400-ampere sockets may be required to accept single or multiple conductors that will carry 200 or 400 amperes.

When aluminum conductors are used, the connectors must be designed for this material; that is, they must not cut the comparatively soft strands and they must not encourage cold flow when the wires are under pressure. If aluminum wire is used in the socket that has plating over the copper connectors, use an aluminum electrical joint compound (antioxidant) to prevent metallic reaction between the alumiun and copper connections.

With the growth of domestic loads and the development of self-contained Class 200 meters, the heavy-duty socket also rated at 200 amperes has been introduced. There are two types of such heavy-duty sockets. In one the jaws are made of massive material and sometimes have only one flexible member.

This may be spring loaded but will still depend on jaw resiliency for good contact. In the other type, the jaws are made of a nonflexible heavy material and the jaws are wrench tightened or lever tightened after the meter is in place. Either type of jaw can carry 200 amperes continuously without excessive heating.

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